Enantiomeric relative abundances

Products 21 and 22 obtained in this reaction differ in their ESI-MS spectra, and the difference in the abundance of respective signals can be expressed quantitatively. Studies have shown that the pseudo-enantiomeric-excess values obtained in this way are in agreement 5% with the data obtained by chromatographic methods, which is sufficient for studying relative values and choosing most selective mutants. 

The application of molecular mechanics to enantio- and diastereo-selective synthesis is less straightforward, and publications in this area have started to appear only recently. In the case of the racemate separations described above, the isomer abundances of equilibrated solutions are taken to be related to the energy of all local minima. In contrast, in order to predict the enantiomeric excesses arising from chiral syntheses, the reaction mechanisms and the basic structure of relevant intermediates or transition states have to be known since their relative energies need to be computed in order to predict the expected enantiomeric excesses. 

There are four diastereomeric menthols according to the relative orientations of the methyl, isopropyl, and hydroxyl groups. They are known as menthol, isomenthol, neomenthol, and neoisomenthol, each of which exists in two enantiomeric forms. The most abundant and readily available is /-menthol, or (/A 2.S, 5iZ)-(-)-menthol (23), whereas other stereoisomers, although available from nature, are more economically produced through chemical derivatizations from menthone, limonene, and a-pinene. Commercial (-)-menthol from natural sources can be as pure as 99% in both chemical and optical purities. Synthetic menthol is currently made by an asymmetric isomerization (see Chapters 12 and 31).34... 

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